Burner and combustion furnace

A burner comprising a multiple pipe including an inner pipe and outer pipes, the inner pipe and the outer pipes being located coaxially about a burner axis, the outer pipes being located outside the inner pipe,

• the multiple pipe including:
• a fuel discharge port which is located at a downstream end of the inner pipe and discharges a fuel-air mixture containing main fuel and primary combustion air which have been supplied to the inner pipe;
• a secondary air outlet which is located at an outer peripheral side of the fuel discharge port and emits secondary combustion air which has been supplied to between the outer pipes;
• and
• an annular gas fuel outlet which is located between the fuel discharge port and the secondary air outlet and emits gas fuel as auxiliary fuel which has been supplied to between the inner pipe and the outer pipes, toward a boundary between flow of the fuel-air mixture and flow of the secondary combustion air.